spectra of adsorbed CO may be assessed. Magic-angle spinning yields precise isotropic shifts and thus could detect subtle changes in the properties of the adsorption site caused by, for example, promoters or coadsorbates. However, magic-angle spinning spectra of adsorbed CO should not be used to exclude the existence of some species. As noted above, the bridge-bonded species do not appear and could be overlooked if the lack of agreement between the center of mass of the broad-line and high-resolution spectra was not noted. The I3C N M R spectra of CO on Rh/silica illustrate another caveat; similar isotropic shifts of the dicarbonyl and linearly bonded CO caused two species to appear as one. To separate these components, it was necessary to decompose the spectra by using sideband intensities predicted from fits to the broad-line spectra. Also, it is tenuous to extract relative site populations from the magic-angle spinning spectra, as seen by comparing the broad-line and high-resolution results in Table I.Measuring both high-resolution and broad-line spectra aids the assignment of component peaks. For example, CO on Ru has at least three isotropic peaks in the range 200-175 ppm, which this study identifies as 199, 195, and 180 ppm. The peak at 199 ppm can be correlated to the Lorentzian peak in the broad-line spectrum by its atypical sharpness (cf. Figure 7) and its lack of sidebands. The other two peaks have sidebands whose intensities and range correspond to linearly bonded CO species. We note that these assignments are inconsistent with an earlier study of CO on Ru/Y ~e o l i t e ,~ which proposed the following peaks and assignments: dicarbonyl (1 68 ppm), linearly bonded CO (1 80 ppm), and bridge bonded (203 ppm). On the basis of the results obtained here, we propose alternate assignments: multicarbonyl (203 ppm), linearly bonded (180 ppm), and linearly bonded (168 ppm). The bridge-bonded species is predicted to lie upfield of 203 ppm and we believe was not resolved, for reasons discussed in preceding sections. V. SummaryHigh-resolution and broad-line I3C N M R spectra of CO on silica-supported Ru and Rh corroborate previous assignments and provide additional information on the adsorbed states. The high-resolution spectra obtained by magic-angle spinning reveal isotropic shifts consistent with the broad-line components proposed previously to be linearly bonded CO and multicarbonyls formed on isolated metal atoms. In addition, experimental evidence suggests two types of linearly bonded CO on Ru/silica. The sharpness of the linear peaks suggests that some Ru and Rh aggregates have negligible magnetic susceptibility, consistent with raftlike structures. Quantitative comparison of the high-resolution and broad-line spectra of adsorbed CO reveals possible pitfalls of relying on magic-angle spinning spectra alone. First, bridge-bonded CO, whose presence is indicated by the quantitatively correct broad-line spectra, is not sufficiently narrowed to be observed in magic-angle spinning spectra. If the I3C NMR spectrum o...

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The oxidation of trimethylphosphine (TMP) to trimethylphosphine oxide (TMPO) has been followed in Y-type zeolites by using 31P MAS-NMR spectroscopy. In a Na-Y zeolite, TMP coordinates weakly with Na+ ions to give a resonance at -59.5 ppm. This form of TMP is readily oxidized at 25 °C to TMPO, which may be coordinated to Na+ (48.6 ppm) or may be physisorbed (41.4 ppm). Similarly, TMP which is weakly bound to a Lewis acid site (-61.5 ppm) in a dealuminated zeolite may be easily oxidized to Lewis-bound TMPO (56 ppm). Liquidlike TMP (-67.1 to -67.9 ppm) is somewhat less easily oxidized, but it also forms physisorbed TMPO. By contrast, the protonated adduct of TMP (-1.0 to -2.8 ppm) is more difficult to oxidize and requires a temperature in excess of 100 °C. TMPO is a weaker Bronsted base than TMP, although the protonated adduct (65, 74 ppm) is formed when TMPO is adsorbed in a H-Y zeolite or when TMP is oxidized in a dealuminated zeolite, which is more strongly acidic.

partment of Energy under Contract DE-AC03-76SF00098, are thanked for HPLC equipment funds. The crystal structure analyses were performed by Dr. F. J. Hollander, UC Berkeley X-ray Crystallographic Facility. We acknowledge the expert help of Drs.